RenderMan Studio supports numerous ways to render a scene. The method you should use depends many things, but most importantly on where you are in your pipeline, what effects you're trying to achieve, and what your render budget is. At the most basic level, RMS renders two ways - offline (e.g. batch rendering a sequence of frames), or interactively (e.g. "re-rendering" during lighting).
When RenderMan for Maya was initially released there was only one mode for PRMan - hybrid rendering, wherein PRMan's ray tracing subsystem could be used with the traditional REYES architecture. Since RMS 4, the RfM plugin has supported PRMan's raytrace hider (introduced in RenderMan Pro Server 16); RMS 18 introduced support for both modes of the raytrace hider - either in path tracing mode or distribution mode. And now RMS 19 introduces RIS, which pushes path tracing to its logical next step, providing uni- or bi-directional path tracing via two built-in integrators: PxrPathTracer and PxrVCM.
Offline rendering is probably the most basic way for a Maya users to render a scene. Hit the Render button and sit back while an image (or a sequence of images) gets written to disk or delivered to a framebuffer (like "it" or the Maya Render View). The RenderMan for Maya plugin can do that, and it can do that in a number of ways. Users can use a Render Preview, with its own settings, for iterative offline renders, or a regular Render with higher-quality settings for "final" renders. These renders can be done with either hider, and with either mode of the raytrace hider.
Renders vs. Previews in Reyes Mode
RMS 19 supports Renders and Render Previews. Fundamentally, each is a "Final" render "pass", but there is a new pass class defined for Render Previews that allows users to use different quality settings for preview and final renders, and then toggle back and forth without having to change multiple settings. Each style of render has its own set of Globals, its own RenderMan Menu item, and its own Options window. Not only can you have different shading rates, pixel samples, and resolutions, you can also do your preview renders locally and then send your final renders to the farm without having to re-open your render options.
Both Renders and Render Previews can use either hider, can be rendered with the internal renderer included with RMS or an external PRMan/RPS, and external renders can be distributed with Tractor. LocalQueue, Alfred, or any queueing system you might happen to use.
Note that this applies only when the RenderMan/Reyes renderer is selected.
Batch Renders also have a separate set of options for the method (internal or external, queueing system, queueing options), but also include a frame range. They use the quality settings for a Render, not a Render Preview, and are initiated via the RenderMan menu, the icon in the RenderMan shelf, or using Maya's batch render mechanisms via the command line.
RenderMan Studio also supports interactive, progressive rendering. Out of the box, it is set up to use the ray tracing modes only. Using the raytrace hider, users can opt to render interactively in path tracing or distribution mode. In these modes virtually any type of edit can be performed, simply and quickly.